CN1632517A

CN1632517A - Probe scanning microscope for tunneling loss and measuring method therefor

Info

Publication number: CN1632517A
Application number: CN 200410077617
Authority: CN
Inventors: 张进修; 丁喜冬; 熊小敏
Original assignee: National Sun Yat Sen University
Current assignee: Sun Yat Sen University; National Sun Yat Sen University
Priority date: 2004-12-28
Filing date: 2004-12-28
Publication date: 2005-06-29
Anticipated expiration: 2024-12-28
Also published as: CN1303415C

Abstract

This invention relates to a dielectric loss scanning probe microscope and its measurement method. The microscope comprises PZT scanning tube, conductive metal probe, non-conductive sample with conductive layer on its down side, scanning tunnel microscope controller, frequency signal generator and phase detector, front amplifier and micro computer. It adopts the bias method of alternating carrier and direct current, which is the following: to choose several work frequency at the peak value of the angle change curve with the alternating amplitude and tunneling loss between the probe and surface to be measured or the place with maximum inclination; to use the tunneling current direct value and tunneling current alternating value and the lag phase angle from the alternating current to the alternating voltage as two-dimensional image display value.

Description

Probe scanning microscope for tunneling loss and measuring method thereof

Technical field

The present invention relates to a kind of surveying instrument and measuring method thereof, particularly a kind of probe scanning microscope for tunneling loss (STDM) and measuring method thereof.

Background technology

Existing probe tunnel flying-spot microscope (STM) all is to work under Dc bias usually, when the distance between probe and tested conducting sample was adjusted to nanoscale (usually all less than 1nm), the Dc bias that is applied caused having between probe and tested conducting sample tunnelling current to take place.By feedback circuit, when keeping distance constant (the permanent height pattern) scanning between probe and tested conducting sample, what obtain usually is the density of states two dimension shape appearance figure on sample surface; By feedback circuit, when keeping constant tunnelling current mode scanning (constant current mode), what obtain is the two-dimensional image of surface relief image-atomic arrangement.Though existing probe tunnel flying-spot microscope has the resolution of atomic level, can not discern what be observed is which kind of atom, molecule or which kind of of bonding.Once there was the alternating voltage that on DC voltage, superposes also to measure the report of tunnel current AC compounent intensity simultaneously, but used apparatus and method are all different with the present invention, do not determine frequency of operation with the variation relation of frequency by the drag angle of measuring current amplitude and electric current, the current hysteresis relief angle that obtains under this frequency of operation also of no use scans the two-dimentional tunneling loss figure of acquisition as feedback quantity or demonstration amount, thereby can not be used for the identification of atom, molecule or of bonding.

Summary of the invention

The purpose of this invention is to provide a kind of probe scanning microscope for tunneling loss (STDM) and measuring method thereof, but the more nano-scale details of measuring samples measured surface can be carried out the identification of atom, molecule or of bonding in the nanometer microcell when utilizing different frequency to scan.

Microscope of the present invention includes PZT scanatron, conducting metal probe, STM controller, prime amplifier and microcomputer system, it is characterized in that on conducting metal probe or sample connecting the frequency of signal generator that can produce the DC component bias voltage and exchange carrier wave, frequency takes place and phase detectors also while and scanning tunnel microscope STM controller be connected with microcomputer system (Fig. 1).

Employing has the bias voltage that exchanges carrier wave and DC component and has substituted Dc bias in traditional scanning tunnel microscope (STM), near the peak value of the electric current-frequency response curve between probe and measured surface and tunneling loss-frequency curve or the slope variation maximum, select several frequency of operation and with the AC compounent amplitude (map of current) of the DC component (shape appearance figure) of tunnelling current, tunnelling current and phase angle (loss figure) that exchange current lags behind alternating voltage demonstration amount as the two-dimensional scan image.

Concrete measuring method is;

1, method with STM is adjusted to nanoscale (usually all less than 1nm) with the distance between probe and tested conducting sample earlier, fix a point again to obtain AC response amplitude I and tunnelling process electric current lagging phase angle δ change curve, i.e. I-f and δ-f curve (see figure 3) with frequency with frequency sweeping.

2, when the sample surfaces atom at fixed point place or structure not simultaneously, the peak value on each bar I-f curve and δ-f curve may be in the different frequency place, the frequency of operation of the frequency that can select slope steepest place on any one frequency peak or the curve during as two-dimensional scan.Certainly, also can select several frequencies to scan simultaneously as frequency of operation.So just can obtain more information.

3, with Dc bias and become under the condition of work of image current, can obtain the STM surface topography map, STDM current amplitude figure and STDM tunneling loss figure at alternating voltage.

Distinguishing feature of the present invention is: the direct current measurement that will have now in the probe tunnel flying-spot microscope makes to exchange and measure simultaneously electric current and loss into.The concrete practice is: earlier with the method for STM keep probe the location and with the distance of measured surface (≤1nm) constant, insert alternate electrical signal and phase angle difference again and measure system, with the sinusoidal pattern AC bias that amplitude is less of Dc bias stack that is added on STM probe or the sample.Because this moment, probe location and it were all constant with the measured surface feature that relates to the distance of measured surface, therefore, the size and the voltage of tunnelling current are approximated to direct ratio, its AC compounent is an exchange current that lags behind voltage on phase angle, and the tangent that electric current lags behind voltage phase angle has promptly characterized the energy loss (Fig. 2) of tunnelling process.The piezoelectric scanning pipe drives probe and moves on sample surfaces in X, Y, three directions of Z under the control of computing machine and feedback circuit, distance and the position of probe on sample between control probe and the sample, thus probe is scanned at sample surfaces.In a two-dimensional scan of probe, can obtain two-dimentional shape appearance figure, AC response current amplitude figure and the tunneling loss figure on measured object surface simultaneously.The details that in two-dimentional AC response current amplitude figure and tunneling loss figure, has demonstrated in two-dimentional shape appearance figure to fail to demonstrate; And different tested atoms demonstrated different gray scales, can be used to the resolution of atom, molecule and of bonding.The present invention can record the various microcell images of scan area from 30 μ m * 30 μ m to 2nm * 2nm according to Testing requirement.

The drawing explanation

Below in conjunction with accompanying drawing the present invention is described in further detail.

Fig. 1 is the structure principle chart of probe scanning microscope for tunneling loss.

Fig. 2 is the synoptic diagram that alternating current lags behind the lagging phase angle of alternating voltage.

More any I-f and δ-f curve that Fig. 3 obtains when being spot frequency scanning.

Fig. 4 is the measurement result that probe scanning microscope for tunneling loss obtains a two-dimensional scan: (A) be STM surface topography map (100nm * 100nm), (B) be that (100nm * 100nm) (C) is STDM tunneling loss figure (100nm * 100nm) to STDM alternating current amplitude figure.

Among Fig. 1, microscope by PZT scanatron 5, conducting metal probe 6, conduction sample 7, have feedback circuit (21), high pressure amplifies scanning tunnel microscope STM controller 2, prime amplifier 4, the phase detectors 3 that have frequency of signal generator (31) and the microcomputer system (band Control Software and display) 1 of (22) and bias voltage stack (23) function and forms.Between conducting metal probe 6 and sample 7 by 23 with scalable DC component bias voltage and the signal that exchanges carrier amplitude on 31 are connected.

Among Fig. 2, ordinate is the relative value of electric current and voltage, and abscissa is phase angle ω t.The position mutually the preceding curve be ac voltage signal, after be AC current waveform, the phase angle that electric current lags behind voltage is labeled as φ in the drawings.

Among Fig. 3, the ordinate of left is current unit pA; Right-hand ordinate is phase angle δ, the degree of unit (degree); Abscissa is a frequency, and unit is KHz.The peak value of I-f curve is in about 27KHz place, and δ-f peak of curve is in about 5KHz place.Therefore frequency of operation all can scan out corresponding two dimensional image near being selected in 5KHz or 27KHz.Select 4.5KHz as frequency of operation in this experiment.

As seen from Figure 4, STDM current amplitude figure (B), STDM tunneling loss figure (C) has and the different details of figure (A) STM surface topography map, does not particularly obtain showing at STM surface topography map (A) in the boundary and the figure (B) of particle, the details of scheming to locate shown in the arrow in (C).As seen the present invention can obtain common scanning tunnel microscope (STM) the details of the nanoscale that can not obtain.In addition, among the two-dimentional alternating current amplitude figure (B) and tunneling loss figure (C) among Fig. 4, homoatomic has not demonstrated different gray scales, can be used to the identification of atom, molecule and of bonding.

Embodiment

Practical measuring examples:

Measuring samples: the part evaporation technical pure copper sheet surface of gold atom

Measuring process:

1, earlier the distance between probe and tested conducting sample is adjusted to nanoscale (usually all less than 1nm), fix a point to obtain AC response amplitude I and tunnelling process electric current lagging phase angle δ change curve, i.e. I-f and δ-f curve with frequency with frequency sweeping.Fig. 3 has provided optional I-f and δ-f curve when a bit.

2, the frequency of operation when selecting near the 4.5KHz of δ-f peak of curve as two-dimensional scan.Certainly, also can select several frequencies to scan simultaneously as frequency of operation.So just can obtain more information.

3, at a-c cycle 4.5KHz, alternating voltage amplitude 25mV; Dc bias 500mV; Become the STM surface topography map (A) that obtains under the condition of work of image current: 0.8nA, STDM current amplitude figure (B) and and STDM tunneling loss figure (C).As shown in Figure 4.

Claims

1, a kind of probe scanning microscope for tunneling loss, it is characterized in that this microscope includes the sample and the microcomputer system of PZT scanatron, conducting metal probe, scanning tunnel microscope controller, prime amplifier, frequency signal generation and phase detectors, conduction, it is characterized in that connecting on conducting metal probe or sample frequency signal generation and the phase detectors that scalable exchanges carrier wave and DC component bias voltage amplitude, frequency signal takes place also to be connected with microcomputer system with the scanning tunnel microscope controller simultaneously with phase detectors.

2, a kind of measuring method of probe scanning microscope for tunneling loss is characterized in that the measuring process of this method is:

1) earlier the distance between probe and tested conducting sample is adjusted to nanoscale after, fix a point again to obtain alternating current amplitude I and tunnelling process electric current lagging phase angle δ change curve, i.e. I-f and δ-f curve with frequency with frequency sweeping;

Frequency of operation when 2) frequency near frequency selection δ-f curve or the I-f curve upward peak or rate of curve steepest place is as two-dimensional scan; Certainly, also can select several frequencies to scan simultaneously, so just can obtain more information as frequency of operation;

3) the alternation carrier wave is being arranged with Dc bias and become the STM surface topography map that obtains under the condition of work of image current, STDM alternating current amplitude figure and STDM tunneling loss figure.